Dynamo-electric machine.



Patented Aug. 27, 1912.

' WITNESSES:

ATTORNEY l subject of the King MILES WALKER, 01 HALE, ENGLAND, MANUFACTURING COMPANY,

ASSIGNOR TO -WESTINGHOUSE ELECTRIC AND A CORPORATION OF IENNSYLVANIA.

DYNAMO-ELECTRIC MACHINE.

mama of Letters latent.

Patented Aug. 27, 1912.

Application filed November 30, 1910. Serial No. 594,998.

To all whom it may concern:

Be it known that 1, MILES WA KER, a of Great Britain, and a resident of Hale, 1n the county of Chester, England, have invented a new and useful. Improvement in Dynamo-Electric Machines, of which the following is a specification.

My invention relates to that type of dynamo-electric machine known as rotary converters, and it has for its object .to provide machines of this type which will withstand excessive overloads without arcing between the positive and negative brushes.

When a dynamo-electric machine is loaded as a direct current generator, the armature current produces a cross magnetic field which tends to weaken the flux at the ed e ofthe pole under which an armature 0011 first moves when it. reaches the pole (called hereinafter the front edge) and to strengthen the flux at the edge under which the coil last moves as it leaves the pole (called hereinafter the rear edge). If the iron of the rear edge and that of the armature teeth under it are magnetically saturated, no great increase of flux therethrough results, while a decrease in the flux through t total flux through the whole pole face is thus decreased, with a consequent reduction 1n thevoltage generated. W hen a direct cur rent generator is short-circuited, th1s weakening of the field causes a drop in the voltage, and the current does not rise to high a value as it otherwise would. This effect is of considerable assistance in avoiding a flash-over from one brush-holder arm to another when a direct current generator is short-circuited. In the case of rotary converter s, however, the reduction in the voltage between the brushes due to the distortion of the flux in the poles is considerably less, since the cross-field which produced by the direct current is to some extent compensated for by the alternating current. Machines of this description are moreover generally provided with damping grids or rings surrounding their pole pieces forthe purpose of preventing sudden distortion or variation of the flux therein, and, consequently, the desiredreduction in the total field flux described above on short-circuit will not occur, even if for a moment the armature is acting as a direct current generator without compensation. Furthermore, if the direct current brushes he front edge is effected. The.

would be fluxes produced by the .the polar projection of a rotary converter are short-circui'oed when the machine is running, the consequent reductlon in the voltage at thealternating current terminals of the machine, caused by the impedance of the alternating current circult, is not of material assistance in preventing an abnormal current fiowthrough the I direct current circuit of the rotary, converter, since the kinetic energy of the rotor of the machine supplies energy to keep the machine running as a direct current generator for a short interval of time. The machine then tends to get out of step, on account of the heavy retarding torque of the direct current circuit of the rotary converter operating as a braking generator.

According to the present invention, the above disadvantages are obviated by providing some or all of the field poles of the rotary converter with ringsor grids of conducting material which surround the rear portions of the pole faces but do not surround the front portions thereof. A. rotary converter thus constructed may or may not amount of inductance in its alternating current circuit which operates in conjunction with the particular arrangement of the pole damping rings to insure both the protection of the alternating current and direct current circuits-of the machine, as will be hereinafter explained.

In the accompanying drawings, Figured is a diagrammatic view, in side elevation, of a portion of a rotary converter, the pole pieces of which are provided with damping grids or rings arranged in accordance with the present invention. Fig. 2 1s a diagrammatic view showing the connections of the machine to the alternatin and direct current circuits. Fig. 3 is a plan view of one of the grids shown in Fig. 1. 1

Referring now to Fig. 1, two of the polar projections of the rotary converter are indicated at l and 2 as connected to a common yoke or frame 8. The armature and commutator of the machine are indicated diagrammatically at 4 and 5, respectively, a positive commutator brush 6 and a negative commutator brush 7 being also shown in the figure. The. path of the magnetic field windings {not shown). of the machine are indicated at l 1 being of north poprojection 2 of south larity and the polar of the cross-magnetic.

polarity. The axes be also-provided with a considerable grid two portions,

fields produced by the current .in the armature windings are indicated at O A, and

thepaths of the fluxes constituting the said cross-magnetic fieldsi'are shown at F Each of the faces of the polar projections 1, 2, is provided with a short circuited ring or 8 of any usual form and of conductin material which surroundsthat portion 0 each pole face under which a point in the armature 4 last moves when it leaves the pole, each pole face being thus divided into viz :the portion indicated at a which is not surrounded by the grid 8 and the portion bwhich is surrounded by the said grid. V

The operation of the apparatus is as follows: When therotary converter is running under normaljconditions, the cross-magnetization which would be produced by the direct current in the armature is neutralized by the alternating current supplied thereto, but if, owing to a short-circuit 'or a sudden decrease in the resistance of the external direct current circuit, the machine delivers a largerdirect current than can be neutralized by-the alternating current, a magneto-motive force is set up along the paths F This magneto-motive force tends to strengthen the flux through the portion 6 of the pole face and to weaken the flux through the portion a. The conducting grid or ring 8, according to a well known manner of operation, serves to retard the rise'in flux through the portion 6 of the pole face which it'sur rounds. There being nothing to oppose the change in the magnetization of the portion a of the pole face, the flux through this portion is reduced under the influence of the armature reaction, or, if the short-circuit be of sufficient-ly low resistance, it may be completely neutralized or even reversed main. pole, under these circumstances, leaks along lateral paths such as F when the said portlon of the flux comesv under the influence of the strong demagnetizing force of the armature current. The voltage gener ated at the direct current brushes is. thus very considerably reduced when a shortcircuit occurs and the current does not rise to as high a value as it otherwise would.

As explained above, the large current due I 'tions of which are provided with low-regsistance members of conducting material the direct current side jlarge reto a short-circuit on of the rotary converter exerts a tarding torque on the rotor of the machine which therefore tends togetEout of step.

. subscribed my name this tenth day of'No-' vember 1910. the current traversing the -short-circuit reinv the manner ex- Witnesses:

This tendency is to a great extent avoided by the use of the grids 8, since, not only is duced by their agency, plained above but, if the short-circuit is still large enou h to effect a reversal of the po larityof t current sides, to limit. the through the slip-rings 10 current side of the apparatus is protected 5 which the flux 1s increased by armature e portions a of the pole faces of the machine, there will .be no great turning movement tending to stop the rotor, since the portions a and Z2 of oppose one another in their magnetic effect.

Referring now to Fig. 2, a rotary converter constructed in accordance with Fig. 1 is shown as having its direct current brushes 6 and 7 connected to a direct current distribution circuit 9, the alternating current sli -rings 10 of the machine being connected t rough inductances 11 to the secondary windings 12 of transformers 13 the primary windings 14 to the conductors of ing current supply circuit 15. The rotary converter, which is indicated as provided with the usual field Winding 16, is thus protected on bothits alternating and its direct since the inductances 11 serve maximum current passing while the direct by the use of thegrids 8 shown in Fig. 1.

It will be understood that the capacity of the gridsor rings 8 may readily be arranged to be suflicient to act as effective amortisseurs or dampers in a well-known manner.

I have thought it unnecessary to describe any specific form of grid or short-circuited -c01l as the construction of these devices is well known in the art and any suitable design may be adopted.

I claim as my invention:

1. A rotary converter having a field magnet pole piece provided with a low-resistance member of conductingmaterial surrounding that portion only of the pole face through re, action so that the flux in the unsurrounded portionmaybe. rapidly varied for the pur- I pose specified.

. in polarity. A portion of the flux from the rent circuit of which as and for the I purpose specifie 3.'A rotary converter the polar projecaround the. rear edge portions only thereof. In testimony whereof, I have hereunto MILES WALKER.-

'F. 'W. LE FALL, A.. S. CAoHnNArLLn.

the pole face substantially 2 its pole pieces provided with low-resistance 1 windings closed upon themselves around the rear edge portions only thereof, 

